1. Field of the Invention
The invention, in general, relates to a hydraulic clutch which is responsive to differences in rotation and which consists of a rotatable input casing, a hydrostatic pump within the casing, an output shaft and a friction clutch for connecting the output shaft to the input casing and, more particularly, to a hydraulic clutch provided with a chamber in which, at the occurrence of a difference in rotations between the input casing and the output shaft, fluid pressure is generated by a pump supplied from a suction chamber for actuating the friction clutch.
2. The State of the Art
Such couplings are used in different configurations in the drivetrains of automotive vehicles for the direct transmission of torque or for blocking an associated differential transmission as well as for powering wheels of an axle or for distributing drive torque between two axles. Each of these couplings utilizes a hydrostatic pump comprising an internal rotor and an external rotor which move relative to each other, and thereby generate fluid pressure, in case the rotations of the input casing and of an output shaft differ.
Hydraulic couplings of this general type are disclosed, for instance, by FIG. 14 of WO 93/19310 and FIG. 12 of U.S. Pat. No. 5,611,746. These couplings are provided with a hydrostatic pump inside of a hollow rotatable casing, and in each case the pump has a pressure and a suction chamber equipped with simple throttles and spring-biased valves responding to predetermined pressures to accommodate certain boundary conditions.
Such arrangements are, however, unsuited for controlling the coupling in a predictable manner. Indeed, such arrangements do not allow adjustments of the transmitted torque relative to differences in rotation or varying temperatures of the operating fluid. These couplings cannot be released when braking with ABS, when the vehicle is being towed, at high speeds or when the clutch is thermally overloaded.